Weather Forecast
A strong ridge of high pressure will persist through the forecast period bringing dry conditions, sunny skies, and warmer temperatures. On Friday/Saturday freezing levels may rise to 2000m in the afternoon, then drop to valley bottom at night. Ridgetop winds should generally be light from the South. Maximum alpine temperatures near -1. Sunday brings alpine sun, valley cloud, and possibly inversions.
Avalanche Summary
No new natural avalanches reported today. Our CAC field team did spend the day out, and investigated some natural slab avalanches that occurred on the 28/29th from Michel Ridge. All three slides were size 3 slab avalanches. One of the avalanches occurred on a East aspect, @ 1965m. The debris was 175m long x 20m wide, with an average depth of 2m. The avalanche consisted of a dense hard slab running on weaker facets below.
Snowpack Summary
Strong SW winds created stiff, yet reactive wind slabs on lee slopes. Cross-loading, and wind slabs are also found lower on the slopes and in unsuspecting terrain due to the strong push of the winds. Below 1700m a 4cm thick crust exists, I suspect it's from the rising freezing levels, and precipitation last Sunday. This crust is said to be supportive. Below this reports indicate the mid-pack to be fairly well settled. Deeper in the snowpack sits the mid-December surface hoar layer. This layer remains a concern for deeper releases. Basal facets and depth hoar also play a major role in this region. In Elk Valley North and the Crowsnest, the average snowpack depth at treeline is 150 cms. Elk Valley S and the Flathead the snowpack depth is closer to 2 m.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.